A typical liquid crystal display device includes an upper substrate, a lower substrate, and a liquid crystal layer between them. The upper substrate has a color filter layer and a common electrode. The lower substrate, referred to as an array substrate, has a switching unit and a pixel electrode. The upper and lower substrates are individually fabricated and then assembled together. Some heating steps, e.g. pre-baking, exposure or post-exposure baking, during the process of forming the upper substrate may lead to deformation of the upper substrate, so that misalignment of the upper and lower substrates may happen during assembly. However, this problem may be solved and the producing process may be simplified by putting a color filter layer and a black matrix layer on the array substrate. Besides, the brightness may be increased since the aperture is improved.
FIGS. 1a and 1b are illustrative diagrams showing a part of an array substrate with a color filter layer according to the prior art. A scan line 500 and a data line 600 intersect with each other on the array substrate 100. A thin film transistor 800 is formed near the intersection. A pixel electrode 900 is formed on a pixel 700 defined by the scan line 500 and the data line 600. A color filter layer 400 lies beneath the pixel electrode 900. A black matrix layer 200 is formed along the scan line 500 to cover the thin film transistor 800. As shown in FIG. 2, a light-blocking black matrix frame 300 is typically formed on the periphery 100a of the display area of the substrate 100 to block light leakage from the backlight.
As shown in FIG. 3, the thickness of the color filter layer 400 formed on the array substrate 100 according to the prior art is different from that of the black matrix frame 300 in the display area. Accordingly, the liquid crystal region 2 over the black matrix frame 300 is thicker than the liquid crystal region 1 over the color filter layer 400, so that gray leveling of light leakage may occur in the liquid crystal region 2. There may be circuits (e.g. driver IC) under the black matrix frame 300 in a low temperature polysilicon (LTPS) LCD. The thickness of the black matrix frame 300 may have to be increased to abate the circuit loading if the dielectric characteristic of the black matrix material is not good. However, increasing the thickness of the black matrix frame depends on the characteristics of the materials, and may be limited since the black matrix layer also exists in the pixel; the display device may then malfunction or have inferior performance.
To eliminate gray leveling of light leakage, there has to be a unique thickness of different liquid crystal regions. Nevertheless, the size of the spacer 1001, sealed by a sealant 1003, must also be modified if the thickness of the color filter layer 400 or the black matrix frame 300 is altered to meet process or product requirements. Then, the producing process would be more complicated. Therefore, a new liquid crystal display device with a simpler producing process is needed to overcome the above-mentioned drawbacks.